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CAC increased, ideal miles decreased

Discussion in 'Roadster' started by asgard, Oct 20, 2013.

  1. asgard

    asgard Member

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    CAC on my car has steadily inched up from 153.3 to 154.0 over two weeks but my ideal miles has dropped from 187 to 184 during the last couple of charges.
    I have been driving more aggressively though, thanks to the Nitron race shocks :)
    Would driving habits cause the ideal miles to drop?
     
  2. djp

    djp Roadster 2.0 VIN939

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    No, driving habits have no effect on ideal miles. The estimated miles take actual driving history into account when projecting range, but the ideal miles only look at battery capacity and state of charge. It sounds like your pack is slightly out of balance with a few low bricks limiting the ideal range. The ideal miles take a while to settle in after the charge is finished, so it might be just be you're looking at the range at different times.
     
  3. asgard

    asgard Member

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    A week ago, I used to get 188 or 189 miles immediately after charging at 240V/40A then it would drop to 186 mi overnight.
    Now it charges upto 186 and settles down to 184 mi overnight.
     
  4. djp

    djp Roadster 2.0 VIN939

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    In that case it's definitely the balancing. I wouldn't worry about it, the CAC is better measure of capacity than ideal miles.
     
  5. asgard

    asgard Member

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    CAC went up a bit more this week. 154.00 to 154.03. Ideal miles is still trending down by about a mile.
    Very weird behavior indeed!
     
  6. Alan

    Alan Member

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    These are pretty small changes so could be do to temperature effects?

    For the ideal miles charging at lower currents gives you a mile or two more. It also depends on when you look, it will be highest just as it finishes charging and drop a few miles over the next couple of hours.
     
  7. asgard

    asgard Member

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    Looks like charging stops at 95-96% SOC so maybe that's why I am seeing lower ideal miles.
     
  8. wiztecy

    wiztecy Active Member

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    95-96% SOC would be a range-mode charge. You mean it was 95-96% complete of a 100% Std. mode charge? CAC is the important number, ideal miles not as much. I've always seen both go up and down independently. And typically the CAC will go down in the winter / cold months and then back up in the warm months from people I've talked to.
     
  9. thefortunes

    thefortunes Member

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    If he is looking at OVMS, the 95-96% is mode-dependent (showing the % of the mode that the car is currently in). The 95%-96% closely matches what I get in Standard mode charging at 32A-40A. If you switch to Range mode or look at the logs, it will show % of total (typically 85% after a Standard charge).

    The reason you are only seeing 95-96% instead of 100% can be described as follows:

    If you are running (i.e. charging at 32A-40A) and try to stop on a line without going over, you might get within a couple feet. If you were walking (i.e. charging at 110v @ 12A-15A) you could stop much closer to the line (and this is borne out by the fact that you will get a few more ideal miles when you charge at 110v).

    Probably a better way to think of it would be trying to fill a pitcher with a firehose vs. a garden hose.
     
  10. asgard

    asgard Member

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    I am looking at the OVMS status. I can try a trickle charge at 110/15A to see if I can squeeze out a few miles, just for peace of mind :)
     
  11. hcsharp

    hcsharp Active Member

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    What is your climate like? My car will usually lose 3 - 5 ideal miles this time of year when ambient temps get colder. The CAC will sometimes change, too. For example my CAC was up slightly this morning but ideal miles were down, just like what happened to you. The only difference that I can see is it was quite cold last night and cold most of the day.
     
  12. asgard

    asgard Member

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    California weather. It was about 66F when I was charging and the coldest was 56.
     
  13. dhrivnak

    dhrivnak Active Member

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    I am not sure this is the case. I have been plotting ideal miles versus standard miles and if I drive the car hard ideal miles WILL drop a little, If I drive very easy I normally see my ideal miles increase. The changes are not large but I am certain they are real. idea_vs_standard.JPG
     
  14. thefortunes

    thefortunes Member

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    Does everyone else have that much variation in their ideal range after charge?

    Mine reports 185/186 every day, however 100 of my 120 average miles per day are commuting so there isn't a significant difference in how I drive from day to day. Maybe that does matter?
     
  15. dhrivnak

    dhrivnak Active Member

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    I find another possible factor in ideal miles is winter/summer. In NE Tennessee I see about 6 miles difference between winter and summer. This could be partially due to lower range overall in winter due to running the heat. Not sure how to separate the two factors easily. Range_Graph.JPG
     
  16. thefortunes

    thefortunes Member

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    Is it possible that you are charging at different amps, taking the reading of ideal miles at different times after charging completes (miles 'settle' over an hour or so), or some other factor?

    I look at your data and am still surprised at the large swings (for example between 9/11 and 10/11 I see what appears to be about 173 miles vs. 184 miles).

    I just had another idea...is this ideal miles USED on a charge vs. ideal miles AVAILABLE after a standard charge? In other words, are you taking how far you drove on a charge and adding the remaining ideal miles and plotting the total, or are you just plotting the total ideal miles after the charge completes (and 'settles')? Because I certainly see the variation in ideal miles USED depending on how I have driven that day, how cold it is, etc...but my ideal miles the next morning after a charge is always the same (+/- 1).
     
  17. Doug_G

    Doug_G Lead Moderator

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    Remember, Ideal miles is an estimate. Your range is how far the car actually goes...
     
  18. djp

    djp Roadster 2.0 VIN939

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    How are you defining "standard miles"? I've seen ideal miles bounce around even when CAC stays the same, and it seems to be related to different SOCs between the bricks. If all bricks are at the same SOC then ideal miles reads higher, but if there's a wide range between the bricks then the system will use the lowest one as a limit.

    I'm not sure what causes the variation in SOC between bricks, but it could be temperature, charge rate, current drawn or depth of discharge. So yes, driving habits might have a slight side effect on ideal range, but it's not directly part of the calculation like projected range.
     
  19. dhrivnak

    dhrivnak Active Member

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    The chart is "ideal" miles and yes it varies at least in my car. I will normally note the range (standard mile) and then hit the VDS to see ideal miles and then record both. I charge at 40 amps at about 2 am. Most days when I record it is about 7am when I leave for work but if I take the bicycle I may not drive until the evening. My Roadster loses about 1 mile per day so the difference between a 7 am drive time and 6 pm is only 1 mile. If I were to show a graph of my standard miles the range would be all over the map as I have seen a low of 55 miles (track day) to 225 miles if I coasted home on a nice day.
     
  20. djp

    djp Roadster 2.0 VIN939

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    Got it, so the scatter plot is Ideal range graphed against Estimated range, both measured after a charge is completed. That is interesting that it has a slope to it, I'm guessing hard driving throws the pack slightly out of balance, which gives you a lower Ideal range.
     

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